The present invention relates to the preparation of lithium hydroxide which is substantially dust free. More particularly, there is provided coated lithium hydroxide monohydrate crystals which are dust free and suitable for producing industrial grease.
Lithium hydroxide monohydrate produces a small amount of dust which is always present when being handled or poured. This dust is extremely choking and irritating to humans even in trace amounts. Large amounts of lithium hydroxide monohydrate are used in industrial grease manufacturing and the choking dust has been a major problem in its use.
Lithium hydroxide has also been used in closed-cycle oxygen systems such as the atmosphere which is found in closed places as submarines or in re-breathing appliances which are used in anesthesia or emergency oxygen equipment because it will react with carbon dioxide. In a rebreather system is it necessary that the carbon dioxide be 4% or less than the entire atmosphere in as much as a greater amount of carbon dioxide will result in a deleterious effect upon the person in the breathing apparatus. The use of lithium hydroxide has been complicated by the fact that anhydrous lithium hydroxide pellets tend to crumble and create noxious dust.
U.S. Pat. No. 3,607,040 to Hevert et al has solved the problem of preventing the crumbling and dust formation of pellets by treating anhydrous lithium hydroxide with polyvinyl alcohol and then calcining the resultant mixture to remove any water. The problem with the use of polyvinyl alcohol is that a unitary treatment of lithium hydroxide is not possible for both powder and pellets since polyvinyl alcohol is not used in the production of grease.
U.S. Pat. No. 2,629,652 to Schecter et al discloses forming porous, anhydrous, non-dusting granules of lithium hydroxide for use in closed space ventilation systems by pressing lithium hydroxide having a water content of between 40 and 45% under pressure of 18,000 to about 25,000 psi to form a cake, breaking the cake into granules and then heating the granules to a moderate elevated temperature. The dust problem is solved because the fine particles which cause dust are physically separated from the granules.
U.S. Pat. No. 2,846,308 to Baxendale disclosed the treatment of alkali hydroxides, which includes lithium hydroxide, with an ester or an organic acid or an ester or an inorganic acid in liquid form to reduce the hydroscopic properties of the alkali hydroxide for use as photographic developers. About 1 to 15% by weight of a lower alkyl acid ester which is liquid and can generate a volatile alcohol is utilized.
U.S. Pat. No. 5,948,736 to Smith et al discloses the coating of lithium monohydrate crystals with fatty acids, esters or triglycerides thereof which require heating to properly coat.
It is an object of the invention to provide a method for reducing the dust when handling lithium hydroxide monohydrate powders and granules without heating.
It is another object of the invention to provide a pourable dust-free lithium hydroxide monohydrate powder.
It is yet another object of the invention to provide a pourable lithium hydroxide monohydrate powder which can be directly utilized to produce an industrial grease.
In accordance with the present invention the above and other objects are accomplished by coating the surface of lithium hydroxide particles and granules with about 0.2 to 1.5% by weight of paraffinic oil, particularly a saturated hydrocarbon oil or a saturate napthenic oil.
Fumed silica in an amount of about 0.01 to 1% weight percent may be added to the composition to enhance flowability.
In one aspect an embodiment of the present invention lithium monohydrate can be made substantially dust free and pourable by the method of adding about 0.2 to 1.5% by weight of a coating of paraffinic oil.
Prefereably, the coating is formed by admixing the lithium hydroxide at ambient temperatures. The paraffinic oils which may be used are those which have a starting boiling point of at least 150xc2x0 C. and a primary boiling point of over about 200xc2x0 C. The paraffin oils are the saturated hydrocarbon oils and saturated napthenic oils including mineral oils of different viscosities.
The paraffinic oils have the advantage over prior coating compositions because they tend to spread evenly at ambient temperatures and do not require heat and subsequent cooling.
These oils are similar and with the base stock oils which are used to make the grease. The coating composition can be applied to the particles in any suitable manner such as by dusting, spraying, grinding or dipping. The coating composition can be mixed with the lithium hydroxide in a tumbler, mixer or other similar apparatus. A solid coating agent may also be dissolved in a suitable solvent sprayed over the lithium hydroxide particles and the solvent then removed in a conventional manner.
In accordance with another embodiment of the invention 0.01 to 1% by weight of composition of fumed silica can be added to improve pourability.